Designed by Appasheb Patwardan in India in the 1940s, takes advantage of a special characteristic of human excreta: feces transmit pathogens, but urine is sterile. The Gopuri separates solid and liquid waste, which occurs naturally in a squatting position. A handful of ashes is sprinkled over the waste after each use. The toilet consists of two vaults. When one is full, it is sealed up, and the adjoining vault is emptied and put into use. The contents decompose anaerobically; the holding period is typically 3-6 months. The urine is disposed of immediately; the compost is used in agriculture.

He also links to an amazing book, Stop the Five Gallon Flush, "the classic 1973 guide from McGill University’s Minimum Cost Housing Group", edited by a certain Witold Rybczynski. It is a wonderful resource; surprisingly, very little has changed in almost 40 years.